Electrical load driving and monitoring circuits are known in the art. One example of such a circuit is described in U.S. Pat. No. 4,574,266 to Valentine. The circuit described therein includes a main electrical load connected in series with a load switch circuit, the series combination being connected across a source of electrical energy. A test circuit and a load detector circuit are both connected to a microcomputer. The microcomputer controls actuation of a switching device in the load switch circuit which, in turn, controls energization of the main load. The circuit described in the '266 patent is capable of detecting electrical conditions of the main load such as an electrical open or an electrical short. When an electrical short condition is detected, the switching device of the load switch circuit is de-energized to disconnect the main load from the source of electrical energy. A load status circuit is provided to indicate the status of the main load and to provide a redundant load in the event of a failure of the main load.
Certain other types of failures can occur in a lamp drive circuit which have not been addressed by prior art circuits. For example, it is possible for a switching device, which is used to connect the lamp to the source of electrical energy, to fail. Also, the signal used to actuate the switching device may become disconnected from the switching device or may become short circuited to a signal which renders it ineffective to actuate the switching device. Furthermore, it is possible for the lamp drive circuit to become disconnected from electrical ground. If any of these types of failures occur, lamp drive circuits known the art would be unable to energize the lamp.